The primary objective is to determine the safety of a multiple IV doses of ABX-IL8 (a humanized antibody directed against IL-8) in the treatment of patients with plaque psoriasis involving greater than 5% of the body surface area. This is a multicenter, randomized, placebo-controlled, dose rising clinical trial examining the safety of administering multiple intravenous infusions of ABX-IL8 in patients with moderate to severe plaque psoriasis. The next dose level will be based on accumulated safety information as defined in the protocol.